JP2003290162A - Pulse-wave measurement apparatus and method for eliminating noise component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pulse-wave measurement apparatus which eliminates noise component derived from the frequency of a commercial power source, and to provide a method for eliminating the noise component. <P>SOLUTION: The pulse-wave measurement apparatus comprises a pulse-wave sensor, filters to filter pulse-wave signals, and a means to measure information on the pulse-wave based on the filtered pulse-wave signals. A first order or a second order analog low pass filter, a preceding digital low pass filter, and a subsequent high-frequency cut-off digital differential filter constitute the filters. The preceding filter is constituted to have a response of approximately zero at either 50 Hz or 60 Hz of the frequency of the commercial power source, and the subsequent filter is constituted to have a response of approximately zero at the other frequency of the commercial power source. The noise component is eliminated by using these filters. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse wave measuring device and a noise component removing method, and more particularly to a commercial power supply frequency when measuring pulse wave information using a fingertip volume pulse wave measuring device and a pulse wave sensor. , A method of removing a noise component derived from its harmonics and other noise components.

[0002]

2. Description of the Related Art In a conventional photoelectric sphygmograph, a fingertip of a subject is placed close to an electrode composed of a photodiode, particularly an anode, and a current amplifier for detecting a photocurrent of the photodiode is used. Since the input impedance of is very high and low, the induced noise from the fingertip of the subject is very likely to get on the output of the current amplifier.
Moreover, since the induced noise from the commercial power supply line is very large in the indoor measurement (see the waveform example with noise shown in Fig. 1), in order to provide a useful pulse wave measuring device, the commercial power supply frequency 50 Hz It is necessary to remove the induced noise that originates from both and 60 Hz.

20 Hz in the effective frequency range for pulse waves
If the cutoff frequency is approximately, the attenuation rate at 50 Hz is -6
Since the analog low pass filter that can be set to 0 dB (1 / 1,000: a negligible attenuation rate with 10-bit resolution) or less is 10th order or more,
It will be expensive. At this time, if the cutoff frequency characteristic is made steep, the ringing-like waveform deformation generated by the stepwise waveform input cannot be ignored.

Acceleration pulse wave (a, b, c, d, e wave)
When the pulse wave information is to be obtained by using, the acceleration pulse wave is obtained by differentiating the original fingertip volume pulse wave twice, so it is necessary to pay sufficient attention to the problems associated with the differentiating process. Generally, in the differential filter, the amplitude of the high frequency component is large in proportion to the frequency, so that there is an advantage that the signal of the high frequency component can be emphasized and viewed. However, at this time, since high-frequency noise also appears to be greatly emphasized, it is necessary to provide a means for clearly distinguishing unnecessary noise from an effective signal and appropriately removing it. Therefore, an accurate analog filter circuit for obtaining this acceleration pulse wave becomes complicated and expensive.

Therefore, it has been conventionally proposed to use a digital filter for removing induced noise. In this case, if the sampling frequency of 100 to 200 Samples / sec (Hz) used in the conventional pulse wave meter is used, the commercial power frequency harmonic (120H
(z, 150 Hz, 180 Hz, etc.) cannot be removed. Also, the order of the digital filter (the number of coefficients) is large, and it is necessary to design a filter with a sharp cutoff frequency characteristic, but as mentioned above, if the cutoff frequency characteristic is made sharp, waveform ringing will occur. .

Therefore, in order to solve the above-mentioned problems, in the photoelectric pulse wave measuring apparatus proposed hitherto, an analog filter having a cutoff frequency of about 10 Hz is actually used. This pulse wave measuring device is usually composed of a high frequency cut filter with a cutoff frequency of about 10 Hz and an analog filter by an analog circuit that performs a differential process to obtain an acceleration pulse wave. As it is, the differential filter is vulnerable to noise derived from high frequencies because the frequency characteristic is proportional to the frequency. Further, in this case, a sharp rising edge, a fluctuation of 10 Hz or more that may appear after closing the ventricle valve, and the like cannot be measured.

Therefore, it is necessary to construct a high-order, high-accuracy, high-frequency cut filter when performing the second-order differentiation process to obtain the acceleration pulse wave, and the conventional pulse wave measuring apparatus is expensive and has a large-scale circuit configuration. Will be. Therefore, as described above, a technique of processing with a digital filter instead of an analog filter has been developed. For example, in a generally widely used photoelectric fingertip plethysmometer, the following processing is performed. , I'm trying to solve it.

For example, a pulse wave amplifier is used as a high cutoff frequency 2
After passing an 8 Hz secondary low-pass filter, 10.
It is configured to pass a 6 Hz primary low-pass filter. A / D converter, sampling frequency 250Sa
mples / sec, digital filter as differential filter, differential filter and low-pass filter
(17th order Finite Impulse Response Filter:
It is called "FIR" filter. ) And is used.

[0009]

In the case of the pulse wave amplifier proposed in the above prior art, the sampling frequency is 25
When a low-pass filter is configured with a 0 Samples / sec FIR filter, it is possible to achieve an induction noise attenuation rate of 60 dB or more when the commercial power supply frequency is 50 Hz. However, since ringing occurs in the frequency characteristics, there is a problem in that the attenuation rate of inductive noise at a commercial power supply frequency of 60 Hz in Western Japan is only about 50 dB.

In the second-order or third-order low-pass filter, the amplitude of inductive noise from the power supply line reaches the amplitude of the volume pulse wave depending on the power supply environment. Therefore, in order to reduce the noise component derived from the commercial power frequency of 60 Hz to 1/100 or less of the amplitude of the acceleration pulse wave, it is about 10,000 times 80 times.
It is necessary to achieve an attenuation rate of dB or higher. If the differential filter is composed of a differential filter, a frequency that is a quarter of the sampling frequency (sampling frequency 250S
In the case of amples / sec, up to 62.5 Hz shows a differential characteristic in which the sensitivity increases with frequency, and the frequency is half the sampling frequency (sampling frequency 250Sampl
In the case of es / sec, it shows a characteristic that the sensitivity becomes zero at 125 Hz. The power supply frequency of 60 Hz is a frequency band about 10 times higher than 5 to 7 Hz which is the main frequency of the acceleration pulse wave. Therefore, from the frequency characteristics of the differential filter, in the acceleration pulse wave, the noise in the 60 Hz band is amplified about 100 times that of the acceleration pulse wave.

When using a digital filter,
As in the above prior art, as a differential filter,
If you use a filter composed of a differential filter and a low-pass filter and increase the amplification factor in a waveform with a small amplitude, the noise of the commercial power frequency cannot be completely removed, and the noise component of the commercial power frequency can be seen in the second derivative waveform. It is the actual situation (see Fig. 1). Further, as a characteristic of the digital filter, noise near the sampling frequency appears by folding back around 0 Hz. Therefore, for example, the noise of the fourth harmonic 240 Hz of the commercial power frequency 60 Hz is 10 Hz.
Appears as noise. An object of the present invention is to solve the problems of the above-mentioned conventional techniques, and a pulse wave measuring device capable of removing a noise component derived from a commercial power supply frequency and its harmonics, and other noise components, and these noise components. The purpose is to provide a method of effectively removing.

[0012]

Means for Solving the Problems The present inventor can estimate the change in the condition of the circulatory system of a subject and the change in the physical condition that causes the change by means of the pulse wave, and thus the pulse wave can be measured with good reproducibility. In addition, we have conducted extensive research and development to eliminate induced noise during measurement. As a result, they realized that by using a pulse wave sensor having a specific configuration and a digital filter, a pulse wave can be accurately measured with good reproducibility without the appearance of induced noise, and the present invention was completed.

The pulse wave measuring device of the present invention comprises a pulse wave sensor for detecting a pulse wave and outputting a pulse wave signal, a filter for filtering and outputting the pulse wave signal, and a pulse wave filtered by the filter. A pulse wave measuring device comprising means for measuring pulse wave information based on a signal, wherein the filter has a cutoff frequency of 20
-30 Hz primary or secondary low-pass analog filter, cut-off frequency 15-40 Hz first stage digital low-pass filter, cut-off frequency 15-
It is composed of a high-frequency cut digital differential filter in the latter stage of 40 Hz, and the digital low-pass filter in the first stage is configured so that the response at one of the commercial power frequency 50 Hz or 60 Hz is near the zero point, and the high frequency in the latter stage. The cut digital differential filter is characterized in that the response at the other of the commercial power frequency is near the zero point. With this configuration, noise components derived from the commercial power supply frequency and its harmonics, and other noise components can be effectively removed.

In the configuration of the above pulse wave measuring device,
The cutoff frequency of the next analog low pass filter is 20 ~
If the frequency is 30 Hz, a desired attenuation factor can be achieved, and ringing-like waveform deformation does not occur in the response to a steep input waveform. Further, if the cutoff frequency of the first stage digital low-pass filter and the wideband cut digital differential filter of the latter stage is less than 15 Hz, performance equivalent to that of the conventional case can be obtained, and the cutoff frequency is 40 Hz.
When it exceeds, ringing (oscillation waveform) occurs in the response to the input waveform with a sharp change.

In the above-mentioned digital low-pass filter at the first stage, when the response at one of the commercial power supply frequencies of 50 Hz and 60 Hz is configured to be near the zero point, the maximum value of the attenuation rate becomes 80 dB (1/1000) or more. In addition to the above configuration, in the latter high-frequency cut digital differential filter, when the response at the other side of the commercial power supply frequency is configured to be near the zero point, the maximum value of the attenuation rate is 40.
It is preferable to configure it to be not less than dB (1/100). In the first stage digital low-pass filter, if the maximum attenuation value is less than 80 dB,
The noise component derived from the commercial power frequency cannot be reduced to 1/100 or less of the amplitude of the acceleration pulse wave, and the induced noise cannot be effectively removed. Further, in the latter high-frequency cut digital differential filter, if the attenuation rate is less than 40 dB, similarly, the induced noise cannot be effectively removed.

The pulse wave sensor is a reflection type pulse wave sensor which measures a pulse wave of a finger of a human body by means of a light emitting section and a light receiving section. On the downstream side, the upper surface of the finger is arranged so as to project from the upper surface of the light receiving section and be higher than the floor surface on which the belly of the finger is placed by a predetermined distance. It is characterized in that a space for mounting on the further downstream side of the arterial blood flow is provided at the tip portion of the floor surface. A pulse wave measuring device incorporating this pulse wave sensor can obtain useful pulse wave information from which noise components derived from the commercial power supply frequency and its harmonics, and other noise components have been removed.

As described above, the light emitting unit is arranged so that its upper surface is higher than the upper surface of the light receiving unit, and the tip of the finger can be attached further downstream of the finger arterial blood flow than the path of the irradiation light. By adopting a structure, the adhesion to the light emitting part of the finger becomes good, and even if the downstream side of the finger blood flow is compressed, the effect on the pulse wave is less than that of the upstream side. The pulse wave information can be obtained with good reproducibility. Further, since the light emitting portion projects from the floor surface, the contact area with the finger is equal to the area of the upper surface of the light emitting portion. On the other hand, when the light emitting part does not project from the floor surface, the contact area between the finger and the floor surface increases. Therefore, to obtain the same contact pressure per unit area as when projecting from the floor surface, The total pressure applied to is greater than that when it is protruding.
As a result, the change in waveform becomes large.

Further, when the light receiving portion is arranged on the downstream side of the arterial blood flow of the finger from the light emitting portion, when a pressing material as described below is provided, it is located on the downstream side of the finger artery blood flow from the pressing portion and the pressing portion. Since congestion occurs, if a light receiving section is provided near this portion, a waveform with poor circulation of peripheral arterial blood flow can be obtained, and proper evaluation cannot be performed.

In the above pulse wave sensor, the light emitting portion has an upper surface which is normally 0.2 to 2. than the floor surface on which the abdomen of the finger is placed.
It is preferable that the height is about 0 mm, preferably about 0.3 to 1.5 mm, and more preferably about 0.4 to 1.0 mm. When the light emitting section is arranged in such a range, the skin surface of the finger pad covers the light emitting section from the upper surface, so that it is possible to reduce the influence of ambient light, leaked light, or reflected light on the measurement data, and the subject When the finger is attached, there is an advantage that the sensor position can be recognized by touching the protruding portion and the finger can be easily placed at a predetermined position. However, if it is less than 0.2 mm, it is difficult to confirm the sensor position, and it is difficult to place the fingertip at a predetermined position, and the influence of reflected light on the measurement data becomes large. Also, if it exceeds 2.0 mm, the skin surface of the finger floats from the floor surface, resulting in an unstable wearing state and the waveform deformation due to the pressure applied to the finger when the finger is placed, resulting in poor reproducibility. However, the measured pulse wave data varies, and it becomes difficult to obtain accurate pulse wave information.

Is the light receiving portion arranged such that the upper surface thereof is at the same level as the floor surface on which the finger pad is placed,
Alternatively, it is preferably arranged so as to be lower than the floor surface by a predetermined distance. Adhesion of the finger to the light emitting portion becomes better. Note that if the light receiving portion is configured to press the finger, congestion will occur at that portion, the circulation of arterial blood flow will deteriorate, waveform changes will occur, and appropriate evaluation will not be possible.
A pressing member is provided on the surface of the space where the tip of the finger is mounted, which faces the floor surface, and the pressing member presses the tip of the fingertip further downstream of the finger artery blood flow than the light emitting portion. The subject is
The fingertips may be consciously or unconsciously put on the fingertip during the pulse wave measurement. In this case, if the subject is instructed to relax, the adhesion to the sensor may deteriorate depending on the shape of the subject's finger. Noise is generated by small movements of the finger both when applying force and when applying force. By providing the pressing member as in the present invention, noise is reduced, reproducibility of measurement data is increased, and accurate pulse wave information can be obtained.

As described above, since the pressing portion of the finger is configured to be limited to a small area on the upper surface of the light emitting portion, the light receiving portion accurately measures the pulse wave of the finger arterial blood flow portion upstream of the pressing portion. can do. When the finger presses the surface other than the top surface of the light emitting unit, even if the pressing site is on the downstream side of the finger artery blood flow,
Since the measurement site of the light receiving unit is affected by the pressure, the reproducibility of measurement is reduced. The side surface of the light emitting portion is surrounded by a cylindrical light shielding wall in order to prevent light emitted from the light emitting portion into the finger from leaking to the outside and to prevent reflected light from the surface of the abdomen of the finger. Is preferred.

The light receiving portion is arranged such that the upper surface thereof is at the same level as the floor surface on which the belly portion of the finger is placed, or is arranged so as to be lower than the floor surface by a predetermined distance. A cushion member is provided on a surface of the space in which the tip is mounted, the surface facing the floor surface, and the cushion member is configured to press the fingertip. The side surface of the light emitting unit is configured such that the light emitted from the light emitting unit into the finger is external. It is surrounded by a cylindrical light-shielding wall in order to prevent light from leaking into the body and to prevent reflected light from the surface of the abdomen of the finger. The side surface of the light emitting portion is surrounded by a cylindrical light shielding wall in order to prevent light emitted from the light emitting portion into the finger from leaking to the outside and to prevent reflected light from the surface of the abdomen of the finger. Is preferred.

The light emitting portion is arranged inside a cylindrical light-shielding wall having an inner surface having a reflection characteristic with respect to irradiation light, and the upper end of the light-shielding wall is usually 0.2 to 2 from the floor surface on which the finger pad is placed. ．
About 0 mm, preferably about 0.3 to 1.5 mm, more preferably about 0.4 to 1.0 mm is projected, and the finger pad is placed on this upper end to cover the entire upper end of the light shielding wall. Is preferred.

When the upper end of the light-shielding wall is projected so as to fall within such a range, the skin surface of the finger pad covers the lower surface of the light-emitting portion from above, so that the influence of ambient light, leaked light, or reflected light on the measurement data is affected. There is an advantage that it can be made small, and when the subject wears his / her finger, the sensor position can be recognized by touching the protruding position of the light shielding wall, and the finger can be easily placed at a predetermined position. However, if it is less than 0.2 mm,
Since it is difficult to confirm the position of the light-shielding wall, it is difficult to place the fingertip at a predetermined position, and the irradiation light from the light emitting unit and the reflected light from the surface of the finger pad easily leak, and the influence of the reflected light on the measurement data increases. Also, when it exceeds 2.0 mm, the finger skin surface floats from the floor surface, resulting in an unstable wearing state,
The pressure applied to the finger when the finger is placed causes the waveform to be deformed, resulting in poor reproducibility, resulting in variations in the measured pulse wave data, making it difficult to obtain accurate pulse wave information.

In the noise component removing method of the present invention, the pulse wave is detected by the pulse wave sensor, the pulse wave signal is output, the pulse wave signal is filtered by the filter and output, and the filtered pulse wave is output. When measuring pulse wave information based on the signal, the pulse wave signal output from the pulse wave sensor is filtered through an analog filter that is a primary or secondary low pass filter with a cutoff frequency of 20 to 30 Hz, and the filtered This pulse wave signal is a first-stage digital low-pass filter with a cutoff frequency of 15 to 40 Hz and a commercial power supply frequency of 50 Hz or 60 Hz.
The volume pulse wave is filtered through a filter configured so that the response on one side is near the zero point, and then the cutoff frequency is 15 to 40 Hz, which is a high-frequency cut digital differential filter at the latter stage of the commercial power frequency. The acceleration pulse wave is further filtered through a filter configured so that the response at zero becomes near the zero point, and the power source frequency riding on the velocity pulse wave and the acceleration pulse wave at commercial power source frequencies of 50 Hz and 60 Hz, and noise derived from the harmonics thereof. It is characterized by removing components.

As the first-stage digital low-pass filter, when the response at one of the commercial power supply frequencies of 50 Hz and 60 Hz is configured to be near the zero point, a filter configured such that the maximum value of the attenuation rate is 80 dB or more is used. When the filter is used to perform filtering, and when the high-frequency cut digital differential filter in the latter stage is configured so that the response on one side of the commercial power supply frequency is near the zero point, the maximum value of the attenuation rate becomes 40 dB or more. It is preferable to perform the filtering using the filter configured as described above.

In the above noise component removing method, the sampling frequency for AD conversion is not particularly critical, and the higher the better. For example, even if an inexpensive microcomputer is used as the control microcomputer and the conversion frequency of the continuous repetitive AD conversion is slow, for example, about 35 kHz, an effective pulse can be obtained if a program such as control processing is taken into consideration. 5 as the sampling frequency to obtain wave information
It is possible to obtain about 00 Samples / sec (Hz) or more.
If the sampling frequency is less than 500 Samples / sec, in order to obtain effective pulse wave information, it is necessary to provide an anti-aliasing filter of order 4 or higher, which complicates the device configuration. Further, the higher the sampling frequency for AD conversion, the more expensive the AD converter is, and the more the amount of filter calculation is required, the longer the digital processing takes. Therefore, the upper limit of the sampling frequency may be set appropriately in consideration of a proper device price, processing time, and the like.

By adopting the sampling frequency as described above, the zero point (maximum point of attenuation rate) of the low-pass filter is set to 50 Hz or 60 Hz of the commercial power source frequency, and the zero point of the low-pass filter is attenuated by applying the attenuation at a high frequency as a differential filter. By using a commercial power supply frequency different from the frequency that is configured to have a zero point, the noise derived from the commercial power supply frequency and its harmonics, and other noise components are effectively removed through the above process. It becomes possible. The pulse wave sensor and the filter used in the noise component removal method of the present invention are as described above.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in comparison with conventional examples with reference to the drawings. According to the analog filter design and circuit example, the first-order low-pass filter
The (LPF) and the secondary LPF can be constructed at low cost because it is sufficient to provide only a few resistors and capacitors for one operational amplifier. FIG. 2 shows an example of a VCVS (voltage control voltage source) type secondary LPF. Cut off frequency of LPF is 30
If the frequency is Hz, the frequency of -50 dB (about 1/300) is about 10 kHz for the primary LPF and about 5 for the secondary LPF.
It becomes 00 Hz. Therefore, the analog LPF is changed to the primary LPF.
Then, the required A / D conversion sampling frequency is 2
It becomes about 0 kHz, and the sampling frequency for A / D conversion required for a second-order LPF is 1,000 Samples / s.
It becomes about ec (1 kHz).

Commercial power frequency in Japan is 50H
Since it is z and 60 Hz, it is possible to provide a useful pulse wave measuring device with a digital filter of 50 Hz and 60 H.
It is necessary to consider a configuration in which z and both are greatly attenuated.
One LPF can be configured so that both the responses at 50 Hz and 60 Hz are close to the zero point, but due to the nature of the digital filter configuration, it has a sharp cutoff characteristic, and the occurrence of ringing cannot be ignored. . Further, in the case of a digital filter, it is difficult to configure it so that it is exactly at the zero point. Therefore, in practice, the attenuation factor is configured to be 80 dB or more, for example.

Therefore, as shown in FIG. 3A, in the first stage digital LPF, one of 50 Hz and 60 Hz is used.
The response at (for example, 60 Hz) is configured to be near the zero point, and as shown in FIG. 3B, in the high-frequency cut digital differential filter, the other frequency (for example, 5 Hz) is set.
It is configured so that the response at 0 Hz) is near the zero point. At this time, it is desirable that the attenuation rate at the commercial power source frequency (for example, 50 Hz) which is not set to the zero point in the digital LPF is 40 dB or more.
With this configuration, in both regions of 50 Hz and 60 Hz, noise derived from commercial power supply frequency and the like can be removed from velocity and acceleration pulse waves. In addition, digital LPF
Commercial power supply frequency region where the zero point was not set in
At (for example, 50 Hz), the noise of the commercial power supply frequency on the pulse wave signal has a practically negligible level.

As described above, the commercial power frequency (60 Hz,
The calculation method of the filter coefficient that makes the response at 50 Hz near the zero point is as follows. FIR (Finite Impulse
Response) The filter coefficient of the digital filter is C
(k), the relationship between the output (y) and the input (x) is
Indicated by.

[Equation 1]

The transfer function H (f) representing the frequency characteristic
Is expressed by the following equation (2).

[Equation 2] (However, in Expression (2), the sampling frequency f _s is 1.)

A time-symmetrical FIR filter has a C
(k) = C (−k).

[Equation 3]

Letting h (k) be the filter coefficient of an ideal filter whose cut-off frequency is f _c , this filter coefficient is expressed by the following equation (4).

[Equation 4] Since the ideal filter causes waveform distortion due to ringing, the filter coefficient of the FIR digital filter is expressed by the following equation (5) using the window function w (k).

[0036]

[Equation 5] The window function w (k), for example, if the Hanning window w _h (k), represented by the following formula (6).

[Equation 6]

By substituting the filter coefficient of the above equation (5) into the equation (3), the frequency characteristic H (f) is obtained. For example, to make the response at a commercial power frequency of 60 Hz zero, the following equation (7):

[Equation 7] Then, f _s , f _c , and N are obtained from this equation. In general, an exact solution cannot be obtained, and an appropriate approximate solution that suits the purpose is adopted.

In the above configuration, when the cutoff frequency of the digital LPF is set to 20 Hz, the analog L
Since both the PF and the digital LPF are configured to have a gentle frequency characteristic in which ringing is extremely small, if the cutoff frequency of the high-frequency cut digital differential filter is set to the higher frequency side, the acceleration pulse higher than 20 Hz The wave signal component can also be evaluated. Further, the sampling frequency is about 500 Samples / sec or more, preferably 5
About 0 to 20,000 Samples / sec, more preferably about 1,000 to 5,000 Samples / sec, the zero point (maximum point of attenuation rate) of the first stage digital LPF is set to 50 Hz or 60 Hz of the commercial power supply frequency, and a digital differential filter As a result, a commercial power supply frequency different from the zero point frequency of the digital LPF is configured to be a zero point by using attenuation at a high frequency, and the commercial power supply frequency and its harmonics are passed through the above process. It is possible to effectively remove noise derived from waves and other noise components, and obtain effective pulse wave information.

The reflection type pulse wave sensor used in the pulse wave measuring apparatus of the present invention will be described below with reference to the drawings. Figure 4
[FIG. 3] is a cross-sectional view showing an example of a structure of a reflection-type pulse wave sensor, (a) is a cross-sectional view showing a schematic structure of a finger mounting part which is a main part of the pulse wave sensor, and (b) is a light emitting part FIG. 3 is an enlarged cross-sectional view of the vicinity of the light receiving portion and the light receiving portion, which is shown with a finger attached.

This reflection type pulse wave sensor has such a shape that a tip of a finger can be attached, and an openable and closable synthetic resin upper portion which constitutes a lid and a finger pad are placed. And a floor portion made of synthetic resin configured so as to be able to. The upper part may have a shape whose inner surface conforms to the outer shape of the finger, and the floor part may have a slightly higher or lower base side of the finger to block ambient light even if the floor surface is flat. It may have an inclined shape so that As described below, a pressing member is provided at the tip of the upper part, and it is possible to press and fix the tip of the fingertip further downstream than the light emitting part of the arterial blood flow of the finger placed on the floor. Further, the light emitting portion and the light receiving portion are arranged at predetermined positions on the floor portion. The pressing member may be any member as long as it can press and fix the tip portion of the finger, and may be, for example, a cushion member or a plate member such as a spring member.
In addition, this sensor includes a current / voltage conversion circuit for reflected light,
If an amplifier is provided and this sensor is connected to a personal computer or the like, the pulse wave measuring device of the present invention can obtain accurate pulse wave information based on the output from the sensor.

In the case of this pulse wave sensor, when a finger is inserted into the finger mounting portion and light such as infrared rays is applied to the abdomen of the tip of the finger, hemoglobin (red blood cells) in the capillaries absorbs part of the light, The amount of light reflected changes (the amount of light reflected decreases in areas with a large amount of blood). Detecting this slight change in the amount of reflected light, converting the detected reflected light from a current to a voltage, transmitting it to an amplifier, and AD-converting the amplified signal voltage using a personal computer, and outputting it. Use as pulse wave information.

As shown in FIGS. 4 (a) and 4 (b), the finger mounting portion forming the main part of the pulse wave sensor has a light emitting diode.
The light emitting unit 1 formed of a semiconductor light emitting device such as (LED) is arranged on the downstream side of the arterial blood flow of the finger 3 of the human body than the light receiving unit 2 formed of a semiconductor light receiving device such as a photodiode (PD).
Looking at the path of the irradiation light 1a from the light emitting unit 1 in the finger, the luminous flux of the light emitting portion diffuses and spreads as it advances in the finger. Therefore, the change in the light amount of the light receiving unit 2 due to the change in the incident light from the light emitting unit 1 is large, and the change in the light amount of the diffused light received due to the change in the position of the light receiving unit 2 is small. Therefore, it is necessary to bring the light emitting unit 1 into close contact with the finger. However, improving the adhesion results in applying extra pressure to the finger. Therefore, in this pulse wave sensor, the light emitting unit 1 is connected to the light receiving unit 2
It should be placed more downstream of the digital arterial blood flow so that excess pressure is not applied to the finger.

The light emitting section 1 is arranged so that its upper surface is higher than the upper surface of the light receiving section 2 by a predetermined distance. That is, the height H ₁ of the light emitting unit 1 is higher than the height H ₂ of the light receiving unit 2 by a predetermined distance. At the tip portion of the finger mounting portion, a space 4 is provided further downstream of the blood flow of the finger artery than the path of the light 1a emitted from the light emitting portion 1 including an infrared LED, and the tip portion of the finger 3 It is configured so that it can be placed in a space.

The surface on which the finger pad of the finger mounting portion is placed is configured as the finger placement floor surface 5. A light emitting unit 1 and a light receiving unit 2 are provided at predetermined positions on the floor surface 5, and the tip portion of the floor surface is inclined and rises so that the tip of the finger can be properly accommodated. In the finger mounting portion, the pressing member 6 is provided on the surface facing the floor surface, which is downstream of the arterial blood flow from the position where the light emitting unit 1 is arranged. The pressing member lightly presses the tip end portion (nail portion) of the attached finger to prevent the attached finger from moving. With this configuration, the subject's conscious and unconscious small movements of the finger are reduced,
Noise generation is reduced, and as a result, changes in the measured waveform are reduced. Even if the pressure material presses the downstream side of the arterial blood flow, the effect on the pulse wave is small.

When the irradiation light 1a from the light emitting section 1 is reflected on the skin surface of the finger and enters the light receiving section 2, the reflected light becomes noise and the amount of light received into the light receiving section 2 varies. For this reason, it becomes impossible to measure an accurate pulse wave. Also,
If the irradiation light 1a leaks to the outside of the pulse wave sensor, the efficiency of the irradiation light is reduced, and the light amount of the reflected light 2a received by the light receiving unit is decreased, which makes it difficult to accurately measure the pulse wave. Therefore, in the present invention, the side surface of the light emitting portion 1 is surrounded by the cylindrical light shielding wall 7 in order to prevent excess reflected light and leakage light.

The light shielding wall 7 may have any shape as long as it eliminates reflected light and leaked light.
A shape such as a cylindrical shape along the outer peripheral shape of the light emitting unit 1 is preferable. The attached finger is in close contact with and fixed to the upper surface of the light shielding wall at the point 7a. The light-shielding wall 7 may be black on the light-receiving portion 2 side, and may have a mirror surface on the inner surface. The material of the light-shielding wall is not particularly limited as long as it has a property of blocking infrared rays. For example, a thermoplastic resin such as polypropylene resin or ABS resin that does not substantially transmit infrared rays, or a black coating on these. The surface-treated product may be used.

In the above pulse wave sensor, an infrared ray permeable insulator cap 8 is provided on the upper surface of the light emitting portion 1, and the light emitting portion 1 and the finger 3 are provided.
It may be arranged so that it does not come into direct contact with. This is to prevent the current-carrying part of the light emitting part from being affected and to prevent the surface of the light emitting part from being cleaned.
The outer shape of the insulator cap 8 may be, for example, a cylindrical shape that follows the shape of the upper portion of the light emitting body 1. If the upper surface of the insulator cap 8 is composed of a concave lens, the directivity of emitted light can be further widened. The material of the insulator cap is not particularly limited as long as it is an infrared transmissive material having high infrared transmissivity, and examples thereof include acrylic resin, polyethylene resin, polycarbonate resin, polystyrene resin and the like. In addition, the light receiving unit 2
So that the finger and the finger 3 do not come into direct contact and pressure is applied to the finger,
It is preferable to have a structure in which a gap is provided between the light receiving portion 2 and the finger 3.

The influence of directivity between the light emitting element of the light emitting section 1 and the light receiving element of the light receiving section 2 is shown in FIG. As shown in FIG. 5 (a), when the light emitting element of the light emitting section 1 and the light receiving element of the light receiving section 2 are arranged in the conventional direction with strong directivity, when the optical axis of the light emitting diode of the light emitting section 1 is displaced, The effective detection area also shifts. However, as shown in FIG. 5B, if the light emitting element of the light emitting section 1 having a weak directivity and the light receiving element of the light receiving section 2 are arranged close to each other, an effective detection area for the deviation of the optical axis of the light emitting diode can be obtained. The gap is relatively small. Therefore, the obtained pulse wave information is accurate. In the pulse wave sensor, the emission angle (half-value angle) α of the irradiation light from the light emitting unit 1 is usually 50 degrees or more,
By setting it to preferably 50 to 85 degrees, and more preferably 50 to 80 degrees, the deviation of the effective detection area becomes relatively small. If it is less than 50 degrees, the deviation of the effective detection area becomes large, and it becomes difficult to obtain accurate pulse wave data.

In the above pulse wave sensor, the longer the distance between the light emitting section 1 and the light receiving section 2, the smaller the amplitude of the a wave, which is the waveform of the acceleration pulse wave, and the more easily the noise component is generated. Deformation tends to be large. Further, as the distance is longer, the pulse wave of the finger part affected by the pressure is measured, and the measured waveform is easily deformed. Therefore, the distance between the light emitting unit and the light receiving unit is set to a predetermined distance, for example, 8
If it is set within mm, preferably within 6 mm, the amplitude of the a-wave of the acceleration pulse wave and the ratio (b / a) of the b-wave to the a-wave fall within an appropriate range. In this case, the deviation of the optical axis is small, the deviation of the effective detection area is small, and the waveform is not easily deformed.
In the finger region on the upstream side of the artery where this distance is outside the above range, the arterial blood vessel swells, resulting in a small b / a (large absolute value), and at the finger region on the downstream side, the congested state. Then, b / a is large (absolute value is small). The lower limit of the distance between the light emitting unit and the light receiving unit is not particularly limited, and may be any minimum distance that can be set depending on the physical size of the light emitting unit and the light receiving unit, the size of the pulse wave sensor, and the like. For example, it may be set to about 2 to 3 mm.

Further, in order to improve the handleability of the pulse wave sensor main body by preventing the insulator cap from falling off,
As shown in FIG. 6, a collar portion 14 a may be provided in the lower portion of the insulator cap 14. In FIG.
Reference numeral 11 denotes a light emitting portion, 11a denotes light emitted from the light emitting portion, 12 denotes a light receiving portion, and 13 denotes a light shielding wall. Light emitting unit 11, light receiving unit 12,
The arrangement positional relationship of the light shielding wall 13 and the like is the same as that shown in FIG. The materials of the light shielding wall 13 and the insulator cap 14 are the same as the materials of the light shielding wall 7 and the insulator cap 8 shown in FIG. Furthermore, if the upper surface of the insulator cap 14 is formed of a concave lens, the directivity of emitted light can be further expanded.

As described above, the light receiving portion is arranged such that the upper surface thereof is at the same height as or lower than the floor surface of the finger mounting portion so that pressure is not applied to the finger. This allows
The finger portion corresponding to the upper position of the light receiving portion where the ratio of the light incident on the light receiving portion is the largest is not pressed. For example, the light receiving unit may be arranged so as to be lower than the finger placement floor surface of the pulse wave sensor by about 1 mm. The pulse wave sensor described above can be connected to a personal computer or the like, and pulse wave information having no noise component can be measured and presented based on the output pulse wave signal from the sensor.

[0052]

As described above, according to the present invention,
A primary or secondary analog low-pass filter with a cutoff frequency of 20 to 30 Hz, a first-stage digital lowpass filter with a cutoff frequency of 15 to 40 Hz, and a cutoff frequency of 15 to 4
It has a filter composed of a high-frequency cut digital differential filter at the 0 Hz rear stage, and is configured so that the response at one of the commercial power frequency 50 Hz or 60 Hz is near the zero point in the first stage digital low-pass filter. The high-frequency cut digital differential filter in the latter stage is configured so that the response at the other side of the commercial power supply frequency is near the zero point, so noise derived from the commercial power supply frequency and its harmonics, and other noise components are removed. It is possible to provide a pulse wave measuring device capable of performing the above.

Further, in the pulse wave sensor for detecting the pulse wave and outputting the pulse wave signal in the device of the present invention, the light emitting portion is located on the downstream side of the arterial blood flow of the finger from the light receiving portion, and the upper surface thereof is the light receiving portion. It is arranged so that it protrudes a predetermined distance above the upper surface and is higher than the floor surface on which the abdomen of the finger is placed by a predetermined distance, and the tip of the finger is higher than the path of the irradiation light from the light emitting part in the finger arterial blood flow. Since a space is provided at the tip portion of the floor surface so that it can be mounted on the further downstream side, the adhesion to the light emitting part of the finger becomes good, and even if the downstream side of the finger artery blood flow is compressed,
Compared to the pressure on the upstream side, it has less effect on the pulse wave,
An accurate pulse wave signal can be obtained with good reproducibility. As a result, the pulse wave measuring device of the present invention can provide accurate pulse wave information with good reproducibility without the appearance of induced noise. Further, since the noise component removal method of the present invention is carried out using the pulse wave measuring device, it is possible to effectively remove the noise derived from the commercial power supply frequency and its harmonics, and other noise components, An accurate pulse wave can be measured with good reproducibility.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of an output waveform by a conventional photoelectric finger plethysmometer, showing an example of a pulse waveform with noise.

FIG. 2 is a circuit example of a VCVS (voltage controlled voltage source) type second-order low-pass filter.

3A and 3B are waveform examples for explaining a design example of a filter used in the present invention, FIG. 3A is a waveform diagram showing a design example of a digital low-pass filter in the first stage, and FIG. The waveform diagram which shows the example of a filter design.

FIG. 4 is a cross-sectional view showing an example of a structure of a pulse wave sensor used in the pulse wave measuring device of the present invention, and FIG. 4 (a) is a cross-sectional view showing a schematic structure of a finger mounting part which is a main part of the pulse wave sensor. , (B) is an enlarged sectional view in the vicinity of the light emitting portion and the light receiving portion.

5A and 5B are schematic diagrams showing the directivity of light in a pulse wave sensor, FIG. 5A is a diagram showing the influence of directivity between a light emitting element and a light receiving element in the prior art, and FIG. 5B is a device of the present invention. FIG. 6 is a diagram showing an influence of directivity between a light emitting element and a light receiving element in the pulse wave sensor used for the.

FIG. 6 is a cross-sectional view showing another example of the structure of the pulse wave sensor used in the device of the present invention.

[Explanation of symbols]

1 Light emitting part 2 Light receiving part 1a Irradiated light 2a Reflected light H ₁ Height of light emitting part H ₂ Height of light receiving part 3 Finger 4 Space 5 Finger resting floor 6 Pressing material 7 Light shielding wall 7a Contact point between finger and light shielding wall 8 Insulator cap 14 Insulator cap 14a Collar α Exit angle of irradiation light (half-value angle)

Claims (9)

[Claims] 1. A pulse wave sensor that detects a pulse wave and outputs a pulse wave signal, a filter that filters and outputs the pulse wave signal, and pulse wave information based on the pulse wave signal that is filtered by the filter. A pulse wave measuring device comprising means for measuring
The filter is an analog filter that is a first-order or second-order low-pass filter with a cut-off frequency of 20 to 30 Hz, a first-stage digital low-pass filter with a cut-off frequency of 15 to 40 Hz, and a high-frequency cut digital differential after the cut-off frequency of 15 to 40 Hz. It consists of a filter and
The first-stage digital low-pass filter is configured so that the response at one of the commercial power supply frequencies of 50 Hz and 60 Hz is near the zero point, and the response at the other high-frequency cut digital differential filter of the latter stage is at the other of the commercial power supply frequency. A pulse wave measuring apparatus, characterized in that is near zero. 2. In the first-stage digital low-pass filter, when the response at one of the commercial power supply frequencies of 50 Hz and 60 Hz is configured to be near the zero point, the maximum value of the attenuation rate is set to 80 dB or more. ,
In the latter-stage high-frequency cut digital differential filter, when the response at the other side of the commercial power supply frequency is configured to be near the zero point, the maximum attenuation value is configured to be 40 dB or more. The pulse wave measuring device according to claim 1. 3. The pulse wave sensor is a reflection type pulse wave sensor for measuring a pulse wave of a finger of a human body by a light emitting section and a light receiving section, and the light emitting section is connected to the arterial blood of the finger from the light receiving section. On the downstream side of the flow, the upper surface of the finger protrudes from the upper surface of the light receiving unit and is arranged to be higher than the floor surface on which the abdomen of the finger is placed by a predetermined distance. The pulse wave measuring device according to claim 1 or 2, wherein a space to be mounted further downstream of the finger arterial blood flow is provided at a tip portion of the floor surface. 4. The light emitting unit is arranged such that an upper surface thereof is higher by 0.2 to 2.0 mm than a floor surface on which the finger pad of the finger is placed, and the light receiving unit has an upper surface of the finger pad of the finger. Is placed so that it is at the same level as the floor on which
Alternatively, it is arranged so as to be lower than the floor surface by a predetermined distance, and a pressing material is provided on a surface facing the floor surface of the space where the tip of the finger is mounted, and the finger material blood The tip of the fingertip on the further downstream side of the flow is configured to be pressed, and the side surface of the light emitting portion is surrounded by the cylindrical light shielding wall, and the light emitted from the light emitting portion into the finger is prevented from leaking to the outside. The pulse wave measuring device according to claim 3, wherein the pulse wave measuring device is configured to block light reflected from the surface of the abdomen of the finger. 5. The light-emitting unit is arranged inside a cylindrical light-shielding wall having an inner surface having a reflection characteristic with respect to irradiation light, and an upper end of the light-shielding wall is 0.2 to 0.2 mm above a floor surface on which a finger pad is placed. 2.0
The pulse wave measuring device according to claim 3 or 4, wherein the pulse wave measuring device is configured so as to protrude by mm, and the belly part of the finger is placed on the upper end to cover the entire upper end of the light shielding wall. 6. A pulse wave sensor detects a pulse wave to output a pulse wave signal, a filter filters and outputs the pulse wave signal, and pulse wave information is measured based on the filtered pulse wave signal. In doing so, the pulse wave signal output from the pulse wave sensor is filtered through an analog filter that is a primary or secondary low-pass filter with a cutoff frequency of 20 to 30 Hz, and the filtered pulse wave signal is cut off with a cutoff frequency. It is a digital low-pass filter in the first stage of 15 to 40 Hz, and has a commercial power frequency of 5
The volume pulse wave is filtered through a filter configured so that the response at one of 0 Hz and 60 Hz is near the zero point, and then the cutoff frequency is 15 to 40 Hz, which is a high-frequency cut digital differential filter in the subsequent stage, the commercial power source. The acceleration pulse wave is further filtered through a filter configured so that the response on the other side of the frequency is near the zero point, and the power supply frequency riding on the velocity pulse wave and the acceleration pulse wave at the commercial power supply frequencies of 50 Hz and 60 Hz, and harmonics thereof. A method for removing a noise component, which comprises removing a noise component originating from. 7. The first-stage digital low-pass filter is configured such that when the response at one of the commercial power supply frequencies of 50 Hz and 60 Hz is near zero, the maximum value of the attenuation rate is 80 dB or more. When filtering is performed using a filter and the latter high-frequency cut digital differential filter is configured so that the response at the other side of the commercial power supply frequency is near the zero point, the maximum value of the attenuation rate is 40 dB or more. 7. The noise component removing method according to claim 6, wherein filtering is performed using a filter configured as described above. 8. A sampling frequency for AD conversion is set to 500.
The method for removing noise components according to claim 6 or 7, wherein the method is performed at Samples / sec or more. 9. The noise according to claim 6, wherein the pulse wave sensor uses the pulse wave sensor according to any one of claims 3 to 5 to detect a pulse wave. Component removal method.